Two-wheel hand truck

ABSTRACT

A sack trolley ( 1 ) comprises a support frame ( 2 ) presenting a lower pair of carrying wheels ( 4 ) and a hoist mechanism ( 6 ) for climbing steps, which comprises a lifting arm ( 10 ) equipped with support rollers at its free end and which can be swivelled about a swivelling axis (S) parallel to the carrying wheel axis (L) by means of a crank drive ( 8 ). In order to achieve step-climbing assistance which is simple, space-saving, easy to handle and functionally safe, the lifting arm ( 10 ) is comprised of a swing guide component ( 11 ) swivel-mounted about the swivel axis (S) and a support component ( 12 ) taking up the support rollers ( 13 ) and longitudinally displaceable compared to the swivel guide component ( 11 ), whereby the crank drive ( 8 ) is articulated on the support component ( 12 ) with its crank arm ( 9 ).

CROSS REFERENCE TO RELATED APPLICATIONS

Applicant claims priority under 35 U.S.C. §119 of AUSTRIAN ApplicationNo. A 1482/98 filed on Sep. 1, 1998. Applicant also claims priorityunder 35 U.S.C. §120 of PCT/AT99/00189, filed on Jul. 28, 1999. Theinternational application under PCT article 21(2) was not published inEnglish.

TECHNICAL FIELD

The present invention relates to a sack trolley having a support framepresenting a lower pair of carrying wheels and upper handles and a hoistmechanism for climbing steps, which comprises a lifting arm equippedwith return rollers at its free end and which can be swivelled about aswivelling axis parallel to the carrying wheel axis by means of a crankdrive.

PRIOR ART

A similar sack trolley is disclosed in EP 0 533 650 B and its hoistmechanism for climbing steps has thoroughly proven itself, whereby thelifting arm designated as support frame engages in a crank guide solidwith the support frame by way of a guide member in its longitudinalcentral region, and its end averted from the free end with the returnroller is articulated on the crank arm of the crank drive. Because ofthe cooperation of support frame, crank drive and crank guide thesupport wheels describe a stilt movement reaching forwards or backwardswith switching on, off and reversing of the drive motor, by means ofwhich the support frame, is lifted as it travels up over the steps withthe carrying wheels over the support wheels now resting on the groundand the support frame is transferred to the next highest step, or as ittravels backwards the support wheels grip downwards on the next loweststep and as a result lower the support frame with the carrying wheels.This hoist mechanism thus requires considerable structural expense andis also associated with a corresponding space requirement which impairsthe handiness of the sack trolley and undesirably increases its tareweight. Further to this, because the centre of gravity is misplacedupwards due to the hoist mechanism there is less stable handling of thetrolley as it climbs steps, and not least of all in tricky situationsthe result is unsafe climbing assistance adapted minimally to the stepprofiles of the step due to the stilt movements of the support wheels.

DESCRIPTION OF THE INVENTION

The object of the invention is therefore to create a sack trolley of thetype mentioned at the outset, which is distinguished by its easilyhandled and functional hoist mechanism with a simple and compactstructure.

The invention solves this task in that the lifting arm is comprised of aswing guide component swivel-mounted about the swivel axis and a supportcomponent taking up the support rollers and longitudinally displaceablecompared to the swivel guide component, whereby the crank drive isarticulated on the support component with its crank arm. The free end ofthe support component is moved on the one hand by the superposition ofthe swivel movement of the swivel guide component effective thereon andthe rotary movement of the crank arm on the other hand along anapproximately reinform curved path, resulting in trouble-free climbingassistance according to the direction of movement with the supportcomponent and its support rollers. When the sack trolley is in aposition corresponding to the travel position the support rollers of thesupport component are set engagingly on the next highest step tread fortravelling up a step, are supported there and raise the trolley from onestep to the other. On the contrary, during descent the support rollersremain supported on the respective upper step and the trolley is loweredby way of the lifting arm to the next lowest step, giving rise to asimple and functionally safe raising and lowering movement for automaticstep travel. The lifting arm with the crank drive can be accommodatedwithout difficulty in narrow spaces, for example between the carryingwheels of the sack trolley, and thereby alters the centre of gravityposition of the sack trolley only insignificantly, in addition to whichthe hoist mechanism does not weigh excessively because of its simplestructure and barely increases the tare weight of the trolleynoticeably. The path of motion of the support rollers is influenced byappropriate adaptation of the crank throw, axle position, lifting armlength, articulation point of the crank throw on the support componentand the like and is adapted to different step profiles, whereby thepassage speeds of the path of the support rollers are adapted to therespective functional areas and the empty run and vertex areas arepassed through more quickly than the lifting or lowering areas requiredfor climbing steps.

A path of motion for the support rollers best adapted to normal use withclimbing steps occurs when the crank axis lies in the direction of thesupport frame above the swivel axis, whereby the crank axis preferablylies above and the swivel axis lies below the swivel carrying wheelaxis, and whereby the distance of the crank axis from-the support frameis preferably greater than that of the swivel axis, and the distance ofthe carrying wheel axis from the support frame is greater than that ofthe crank axis.

To facilitate assembly of the hoist mechanism and also to be able tosubsequently alter the curved path for the support rollers the hoistmechanism plus the crank drive and lifting arm are designed as assemblyunit and attached displaceably to the support frame, such that theassembly unit can be mounted problem-free with few hand grips and can beadjusted in place, leading to change in position of the swivel and crankaxes and thus to relative displacement of the curved path of the supportrollers.

It is particularly advantageous if the support rollers of the supportcomponent are equipped with a combined free-wheel and brake device whichreleases rotating of the support rollers in terms of the trolleytravelling backwards, but which brakes counter-rotation of the supportrollers. Release of the rotary movement of the support rollers in onedirection and their braking instead of blocking in the counter-rotationdirection facilitates climbing steps with the assistance of the hoistmechanism, since the position of the support rollers on the steps can becorrected effortlessly by the driver of the trolley without losing thenecessary support effect of the support rollers.

BRIEF DESCRIPTION OF THE DRAWINGS

The inventive object is illustrated purely schematically in the diagramwith reference to an embodiment, in which:

FIG. 1 shows a sack trolley according to the present invention in sideview, whereby the front carrying wheel has been omitted for the sake ofclarity,

FIG. 2 shows a cross-section along line II-II of FIG. 1 on an enlargedscale,

FIG. 3 shows the hoist mechanism of the sack trolley according to thepresent invention in side view on an enlarged scale with a motiondiagram, and

FIG. 4 shows a support roller of the hoist mechanism in axial section onan enlarged scale.

METHOD FOR CARRYING OUT THE INVENTION

A step-climbing sack trolley 1 comprises a support frame 2 whichexhibits upper hand grips 3 for handling and lower carrying wheels 4 forground support. Carrying wheels 4 rotating about a horizontal carryingwheel axis L are borne on lateral carrying wheel supports 5, such thatthere is space for arranging a hoist mechanism 6 inside the carryingwheels for climbing steps. Said hoist mechanism 6 comprises a crankdrive 8 operated by a battery-powered drive motor 7, whose crank arm 9is articulated on a lifting arm 10. Lifting arm 10 comprises a swivelguide component 11 swivel-mounted about a swivel axis S parallel tocarrying wheel L and a support component 12 longitudinally displaceableopposite this swivel guide component 11, on which crank arm 9 of crankdrive 8 engages and whose free end bears support rollers 13.

In the illustrated embodiment support component 12 is designed as abracket and crank drive 8 is articulated on both legs 121, 122 ofsupport component 12 with crank arms 9 arranged in pairs. However, oneleg 121 only of support component 12 is guided to be displacedlongitudinally on a branch-shaped swivel guide component 11. Supportrollers 13 rest in the end region of both bracket legs 121, 122 on axlestubs 14, whereby each support roller 13 is equipped with a combinedfree-wheel and brake device 15. As illustrated in FIG. 4, a wheel hub 16is borne on one side by a roller bearing 17 and on the other side by afreewheeling hub 18 on axis stub integral with the support component,such that free-wheeling hub 18 releases wheel hub 16 in one direction ofrotation, shown here in the backwards travel direction of the trolley,and in the other direction of rotation it is barred by jamming with axisstub 14. Said free-wheeling hub 18 is fitted as is customary withjamming rollers 19 and accordingly requires no further explanation. Awheel rim 20 with suitable tyre 21 sits on wheel hub 16, which isconnected non-positively to wheel hub 16 by means of a brake 22. Brake22 comprises a brake disc 23 torsional compared to wheel hub 16, whichis pressed against an annular stop 25 of wheel rim 20 by means of aspring-loaded tension device 24 with a specific pretension, such thatwhen resulting frictional forces are surmounted relative rotationbetween wheel rim 20 and brake disc 23 or wheel hub 16 is possible. Ifsupport roller 13 is rotated in the locking direction of free-wheelinghub 18, wheel hub 16 blocks opposite axis stub 14 and it now depends onthe absorbing torque as to whether wheel rim 20 remains torsional withtyre 21 as compared to wheel hub 16 under the effect of brake 22, ordescribes a braked rotational motion.

As indicated in FIG. 3, the interplay of crank drive 8 on the one handand lifting arm 10 with support component 12 longitudinally displaceableon the swivel guide component on the other hand gives rise to anupright, substantially reniform path of motion B, for support rollerssitting on the free end of the support component, which moves pastsupport rollers 13 on the return stroke on the step profile whenclimbing the steps, but which sets down on the respective steps on theworking stroke and then raises or lowers sack trolley 1. According toFIG. 3 sack trolley 1 is in its step-travel position, whereby liftingarm 10 is directed in its starting position approximately normally tosupport frame 2 (position 1). If a step is now ascended by sack trolley1, it is brought up against the step and crank drive 8 is switched on inthe direction of rotation of movement arrow H so that support rollers 13are first drawn back along curved path B and then moved upwards andfinally set down on next highest step T (position 11), by means of whichfurther swivelling of lifting arm 10 raises the entire sack trolley overthe step profile to the next highest step tread T. In the processfree-wheel brake device 15 of support rollers 13 prevents the supportrollers from rolling back down the steps undesirably, though it doesallow the trolley to be pulled further up the steps at any time.

When it descends the steps sack trolley 1 is pulled on an upper step Twith carrying wheels 4 sufficiently far over the step edge that supportrollers 13 set down on step T and by means of the loading switch on thedrive of crank drive 8 which moves lifting arm 12 in the direction ofmotion arrow U (position III). Hoist mechanism 6 thereby lowers sacktrolley 1 down from one step to the other, whereby the sack trolley ismoved around the step edges on account of path of motion B of supportrollers 13. Free-wheel brake device 15 of support rollers 13 alsofacilitates the backward movement of the sack trolley.

A favourable form and position of path of motion B for support rollers13 occurs whenever, in the longitudinal direction of support frame 2swivel axis S with distance a lies below carrying wheel axis L and crankaxis K with distance b lies above carrying wheel axis L, and whendistance d of crank axis K from support frame 2 is greater than that cof swivel axis S, and distance e of carrying wheel axis L from supportframe 2 is greater than that d of crank axis K.

Hoist mechanism 6 together with crank drive 8 and lifting arm 10 isarranged adjustably to influence the relative position of path of motionB, and is for example attached to swivel adjustably by means of a dragbearing 26 and a longitudinally adjustable support strut 27 to supportframe 2, such that the path of motion is altered relative to the supportframe by means of a swivel adjustment of this assembly unit.

What is claimed is:
 1. A sack trolley comprising (a) a support frameextending in a longitudinal direction and having an upper end and alower end, (b) hand grip means at the upper end of the support frame,(c) a pair of carrying wheels at the lower end of the support frame, thecarrying wheels being rotatable about axes extending transversely to thelongitudinal direction, and (d) a hoist mechanism mounted on the supportframe between the carrying wheels for climbing steps, the hoistmechanism comprising (1) a lifting arm having one end comprised of aswing guide component which may be swivelled about a swivel axisextending parallel to the axes of the carrying wheels and a supportcomponent at a free end opposite to the swing guide component, thesupport bracket component being longitudinally displaceable relative tothe swing guide component and comprising a pair of legs and a supportportion extending between the legs transversely to the longitudinaldirection, (2) support rollers on the support bracket component, and (3)a crank drive comprising two crank arms linked to the legs of thesupport bracket component and having a crank axis arranged above theswivel axis of the swing guide component.
 2. Sack trolley as claimed inclaim 1, wherein the distance of the crank axis from the support frameis greater than the distance of the swivel axis from the support frame,and the distance of the carrying wheel axes from the support frame isgrater than the distance of the crank axis from the support frame. 3.Sack trolley as claimed in claim 1, wherein the hoist mechanismincluding the crank drive and the lifting arm is an assembly unitattached adjustably to the support frame.
 4. The sack trolley of claim1, wherein the crank axis is arranged below the axes of the carryingwheels.